
<PAGE>
 
                                                                      EXHIBIT 24

                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Richard S. DeVine            Director 
-----------------------------
Richard S. DeVine
<PAGE>
 

                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Jack Fabulich                Director 
-----------------------------
Jack Fabulich

<PAGE>
 

                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Jonathan Fine                Director 
-----------------------------
Jonathan Fine
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ John P. Folsom               Director 
-----------------------------
John P. Folsom
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Margel S. Gallagher          Director 
-----------------------------
Margel S. Gallagher
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ John A. Halleran             Director 
-----------------------------
John A. Halleran
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Thomas L. Matson             Director 
-----------------------------
Thomas L. Matson
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ John H. Powell               Director 
-----------------------------
John H. Powell
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Robert E. Quoidbach          Director 
-----------------------------
Robert E. Quoidbach
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Donald Rodman                Director 
-----------------------------
Donald Rodman
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Frank H. Russell            Director 
-----------------------------
Frank H. Russell
<PAGE>
 

                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ Sidney R. Snyder             Director 
-----------------------------
Sidney R. Snyder
<PAGE>
 


                               POWER OF ATTORNEY

     The director of Columbia Banking System, Inc. (the "Company"), whose
signature appears below, hereby appoints W. W. Philip and J. James Gallagher, or
either of them, as his attorney to sign, in his name and behalf and in any and
all capacities stated below, the Company's Form 10-K Annual Report pursuant to
Section 13 of the Securities Exchange Act of 1934, and likewise to sign any and
all amendments and other documents relating thereto as shall be necessary, such
person hereby granting to each such attorney power to act with or without the
other and full power of substitution and revocation, and hereby ratifying all
that any such attorney or his substitute may do by virtue hereof.

     This Power of Attorney has been signed by the following person in the
capacity indicated, on the 25 day of February, 1998.


Signature                        Title


/s/ James M. Will                Director 
-----------------------------
James M. Will
